1. Field of the Invention
The invention relates to a circuit arrangement comprising an integrated circuit in which a microprocessor is provided which controls an index generator provided in the integrated circuit for teletext and/or on-screen display functions and which performs control functions of a television apparatus by means of a control interface provided in the integrated circuit.
2. Description of the Related Art
Such an integrated circuit is marketed by Philips under the type name SAA 5290. This circuit includes a microprocessor which is capable of taking over control functions for the television apparatus in which the integrated circuit may be incorporated. Moreover, a decoder for teletext functions is provided in the integrated circuit. This decoder is implemented as hardware. The circuit is capable of taking over so-called on-screen display (OSD) functions such as, for example the display of the adjusted sound volume. The software required in the IC, particularly for the microprocessor, is contained as a ROM in the IC. This software cannot be adapted to changing ambient conditions. A given type of such an integrated circuit is thus not suitable for different apparatuses or for different purposes.
It is an object of the invention to improve the circuit arrangement described in the opening paragraph in such a way that a more universal use and a simpler adaptation to other conditions is possible.
According to the invention, this object is solved in that a storage interface for a read-only memory outside the integrated circuit is provided in the integrated circuit, and in that the read-only memory comprises at least a part of the program code for the microprocessor and at least a font for the teletext function and possible further index functions.
In the circuit according to the invention, a read-only memory (ROM) is provided outside the circuit, which memory comprises at least a part of the program code for the microprocessor and the fonts or characters required for the teletext functions or on-screen display functions, respectively. Moreover, a ROM may be provided in the integrated circuit which is suitable, for example for those parts of the program code which are independent of the circumstances in which they are used.
The external read-only memory has the advantage that it can easily be exchanged and thus a simple adaptation to different apparatuses or ambient conditions can take place. The integrated circuit as such may thus always be implemented in an identical manner, which reduces its cost. An adaptation to different environments, for example different types of television apparatuses for which the circuit arrangement is provided, then only leads to an adaptation of the code in the read-only memory. Thus, an updating of changed ambient conditions is also easily possible in this way.
The number of external components is limited in that only one read-only memory is provided for the program code for the microprocessor, or at least parts of the program code, and for the fonts and characters for the teletext functions and/or on-screen display functions.
In accordance with an embodiment of the invention, operating system software is provided for the microprocessor, which software is at least partly stored in the external read-only memory and has a software interface on which the application programs can be set up, which are stored exclusively in the external read-only memory.
To provide universal use of the microprocessor and hence the entire integrated circuit, an operating system software is provided for the microprocessor which can be directly set up on hardware of the microprocessor. This operating system software as such still does not provide the required functions for the on-screen display, teletext functions or control of the television apparatus. The operating system software serves as a basis for application software set up on this software, which application software then realizes the required functions. The hardware-oriented operating system software may be partly provided in the integrated circuit and partly in the external read-only memory. It is advantageous to provide those parts of the operating system software, which are time-critical, within the integrated circuit and to store the less time-critical, i.e. slower parts of the operating system software in the external read-only memory. In any case, the application software to be set up on this operating system software is provided for application programs in the external read-only memory. The advantage of a quick adaptation to changed or different circumstances of use is then maintained, because in these cases only the application programs or the application software as such, which are stored in the external read-only memory, are to be changed. The hardware-oriented operating system software remains unchanged, so that it is unimportant whether a part of this software is stored in the read-only memory provided in the integrated circuit.
In accordance with a further embodiment of the invention, the integrated circuit is provided with a data reception unit via which teletext data and possible further data are received from an external signal source, particularly a receiving unit of a television apparatus, said data being identified and A/D converted in the data reception unit, and in that the digital data supplied by the reception unit of the integrated circuit are decoded in a software-controlled manner by means of the microprocessor and further processed.
To process teletext data, the picture lines of a television signal are applied to the data reception unit in the integrated circuit from a reception unit of a television apparatus. The data reception unit determines the lines which comprise teletext data or other data. An AID conversion of the picture lines comprising these data takes place in the data reception unit. The data are then made available within the integrated circuit. The teletext data are decoded in a software-controlled manner, i.e. a hardware decoder is not provided but the decoding takes place by means of the microprocessor and a corresponding program.
In accordance with a further embodiment of the invention, the index generator is implemented for building up arbitrary graphics, whose output data are applied to the integrated circuit from the exterior, particularly from the external read-only memory, and which are further processed in the integrated circuit.
The data for the build-up of such graphics are preferably stored in the external read-only memory. They are read from this memory and further processed in the integrated circuit under the control of the microprocessor. Thus, there is also the advantage that such graphics can be easily changed, namely by a different programming of the external read-only memory.
In a further embodiment of the invention, arbitrary pixel graphics are generated in a software-controlled manner by means of the microprocessor from output data stored in the external read-only memory, which pixel graphics have a preselectable pixel and color resolution and, possibly after temporary storage, are given a format which is suitable for indication by means of the indication unit.
Graphics stored in the external read-only memory may be further processed in the integrated circuit. This provides a versatility of indication possibilities which can relatively easily be realized due to the structure of the integrated circuit. Controlled by the microprocessor or a software program, the pixel graphics stored externally in their original form are further processed within the integrated circuit so that new graphics are produced. Due to its structure, the circuit arrangement is capable of generating or further processing high-resolution pixel graphics. Advantageously, the externally stored graphics may be accompanied by information about the pixel and color resolution. The further processed high-resolution graphics may be temporarily stored within the integrated circuit and, by means of the indication unit, they may subsequently be given a format which can be further processed and indicated by the television apparatus. The circuit arrangement according to the invention thus provides the possibility of displaying high-resolution graphics in any arbitrary form on a television apparatus. This may be done, for example for on-screen display purposes, but it is also possible to generate effects, improved graphics for teletext functions, or the like in this way.
In a further embodiment of the invention, a storage unit may advantageously be incorporated in the integrated circuit for temporarily storing high-resolution graphics. This storage unit may also be used for storing a graphic cursor. Such a graphic cursor has no fixed predetermined shape but may have different shapes which are stored in the storage unit. The shape of the cursor may thereby be adapted for the relevant indication situation.
In a further embodiment, a data decoder for special functions such as, for example, Hamming decoding, CRC error correction or decrypting encrypted programs is provided in the integrated circuit. Due to the integration of such a data decoder, a corresponding external circuit is not required. The internal data decoder may be used for different purposes and is thus universally applicable.
In a further advantageous embodiment of the invention, the decoder may continuously subject data supplied thereto to the decoding process. The output data of the decoder are only requested when encoded data are concerned. This has the advantage that data can immediately be made available in a decoded form by the decoding unit as soon as data in a decoded form are recognized. If the decoding process did not proceed continuously, it would be necessary to supply coded data to the decoder once more when these coded data are recognized so that this decoder can perform the decoding operation. This resupply of data will be superfluous because the decoding process proceeds continuously and thus decoded data can be called for any time.
In accordance with a further embodiment of the invention, the integrated circuit is provided with a synchronizing unit which generates clock signals of different frequencies required in the integrated circuit from an externally supplied clock signal. The externally supplied clock signal may be supplied, for example, by a quartz oscillator. The synchronizing unit generates various clock signals of different frequency within the circuit from this externally supplied clock signal.
In accordance with a further embodiment of the invention, the synchronizing unit varies the frequency of the clock signals generated for the index generator, dependent on the index parameters of a selected graphic standard. The above-mentioned high-resolution graphics may have different index formats, for example, graphics having an aspect ratio of 16:9 or 4:3, but the graphic resolution may also vary and, dependent on the parameters of this indication, different clock frequencies will be required. The synchronizing unit applies clock signals with a frequency adapted to the parameters of the index format to the index generator.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.